This section provides background information related to the present disclosure and is not necessarily prior art.
Many modern combustion engines include an exhaust gas recirculation (EGR) system. Exhaust gas recirculation is an emission control technology allowing significant NOx emission reductions from diesel engines. EGR is also used in gasoline engines in order to eliminate fuel enrichment at high loads to increase engine efficiency. In both cases, the EGR takes effect by reducing combustion temperature, primarily through dilution effects (lowering the oxygen concentration in the combustion chamber), thermal effects (heat absorption) and chemical effects of CO2 and water in the EGR. The present disclosure uses CO2 separated from exhaust gas and uses it as EGR working fluid. CO2 effects in EGR gas have been illustrated by Ladommatos et al. (Ladommatos, N., S M. Abdelhalim, H. Zhao, Z. Hu, 1996. “The Dilution, Chemical, and Thermal Effects of Exhaust Gas Recirculation on Diesel Engine Emissions—Part 2: Effects of Carbon Dioxide”, SAE Technical Paper 961167, doi:10.4271/961167), herein incorporated by reference. In addition, EGR is also used on gasoline engines at part loads to reduce pumping work. CO2 separated from exhaust gas can also be used for that purpose. It can also be used as EGR replacement on any internal combustion engines. Such EGR systems may include one or more EGR conduits and one or more EGR valves that recirculate filtered or unfiltered exhaust gas back to the engine to be mixed with intake air and fuel for combustion in the engine. While such EGR systems have generally performed adequately for their intended purposes, there remains a need in the art for continuous improvements in engine performance and cleaner engine emissions.